Semiconductor device and method for manufacturing the same

ABSTRACT

A semiconductor device includes a gate insulating film formed on a silicon substrate, a gate electrode formed on the gate insulating film, and an electrical insulating film formed on the gate electrode. The electrical insulating film includes a N—H bond and substantially no Si—H bond. The electrical insulating film is formed by using tetrachlorosilane (SiCl 4 ) that contains no hydrogen (H) as a source gas for a silicon nitride film. Thus, the semiconductor device can suppress residual hydrogen in the gate insulating film and prevent interface defects of the gate insulating film, a shift in the threshold voltage of a transistor, and the degradation of an on-state current. A method for manufacturing the semiconductor device also is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method formanufacturing the semiconductor device. In particular, the presentinvention relates to a semiconductor device that includes a thin gateinsulating film and a method for manufacturing the semiconductor device.

2. Description of the Related Art

In LSIs (large scale integrated circuits), miniaturization of theelements, i.e., MOSFETs (metal oxide semiconductor field effecttransistors) and a decrease in operating voltage have been pursued toincrease the degree of integration per chip. With the achievement ofhighly integrated elements, a polymetal gate that uses a tungsten filminstead of a tungsten silicide film for word lines has been studied toimprove the speed of the elements. The specific resistance of thetungsten film is even lower than that of the tungsten silicide film.

For example, JP 11(1999)-261059 A discloses a method for fabricating asingle p-channel MOS (metal oxide semiconductor) transistor thatincludes a polymetal gate with a conventional LP-SIN (low pressurechemical vapor deposition silicon nitride) film by using a STI (shallowtrench isolation) process. FIGS. 9A to 9D are cross-sectional viewsshowing the method in order. First, shallow trenches for isolation (STI)161 are formed in a substrate 141, and then an n well 151 is formed byion implantation of phosphorus (P) and arsenic (As) into a regionbetween the trenches (FIG. 9A).

A RTP (rapid thermal process) is performed to form a gate insulatingfilm 11 of an oxide film or oxynitride film. Using a LPCVD (low pressurechemical vapor deposition) chamber, an amorphous Si film 12 is grown ina SiH₄ atmosphere, and then is doped with boron (B) by ion implantation.A titanium nitride (TiN) film 14 and a tungsten (W) film 15 aredeposited in the order mentioned. A LP-SiN film 16 that serves as agate-cap layer is formed on the tungsten film 15 in an atmosphere ofSiH₂Cl₂ (dichlorosilane, which may be abbreviated as “DCS” in thefollowing) and NH₃. On top of that, a photoresist pattern 17 is formedto provide a gate pattern (FIG. 9B). The boron-implanted amorphous Sifilm 12, the titanium nitride film 14, and the tungsten film 15constitute a gate electrode 18 in the subsequent process.

By using the photoresist pattern 17 as a mask, etching is performed toform a polymetal gate (gate electrode) 18 (FIG. 9C).

A side wall 19 is formed with the LP-SIN film. The side wall 19 is usedto provide a LDD (lightly doped drain), a source (p⁺) 171, a drain (p⁺)172, etc. (FIG. 9D).

For the polymetal gate thus produced, however, a large amount ofhydrogen (H) is included in a range from the surface of the gate caplayer 16 to a depth of about 125 nm (FIG. 10). In FIG. 10, thehorizontal axis indicates a depth (nm) from the surface of the LP-SINfilm 16 (the gate cap layer) shown in FIG. 9D, and the vertical axisindicates the hydrogen concentration (atoms/cm³). The LP-SiN film 16 isformed of a SiH₂Cl₂ gas including a Si—H bond and a NH₃ gas including aN—H bond. Therefore, unreacted Si—H and N—H bonds remain in the siliconnitride film, so that a large amount of hydrogen (H) is entrapped. Theunreacted Si—H and N—H bonds are separated by various heat treatmentsafter the deposition of LP-SiN to generate hydrogen. This hydrogendiffuses into the gate insulating film and acts as an electron trap,causing a shift in the threshold voltage (Vth) of a MOSFET and thedegradation of an on-state current (Ion).

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide a semiconductor device that can suppress thediffusion of a large amount of hydrogen (H) into a gate insulating filmand prevent a shift in the threshold voltage of a transistor and thedegradation of an on-state current, and a method for manufacturing thesemiconductor device.

A semiconductor device of the present invention includes a gateinsulating film formed on a silicon substrate, a gate electrode formedon the gate insulating film, and an electrical insulating film formed onthe gate electrode. The electrical insulating film includes a N—H bondand substantially no Si—H bond.

The electrical insulating film that includes substantially no Si—H bondis defined as not having a peak of Si—H stretching in a wave numberrange of 2100 to 2500 cm⁻¹ measured by a Fourier transform infraredspectrometer (FT-IR), or even if the film has the Si—H stretching peak,the peak is negligibly minute amount.

A method for manufacturing a semiconductor device includes forming agate insulating film on a silicon substrate, forming a gate electrode onthe gate insulating film, and forming an electrical insulating film onthe gate electrode. The electrical insulating film is formed so as toinclude a N—H bond and substantially no Si—H bond by decomposition anddeposition of a mixture of a gas including substantially no Si—H bondand a gas including a N—H bond.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are cross-sectional views showing the processes of amethod for manufacturing a semiconductor device of Embodiment 1 of thepresent invention.

FIG. 2 is a graph showing a hydrogen bond in silicon nitride films,which is measured by a Fourier transform infrared spectrometer (FT-IR).The silicon nitride films are produced respectively by a method ofEmbodiment 1 of the present invention and a conventional method.

FIG. 3 is a graph showing the hydrogen distribution of silicon nitridefilms having a polymetal gate structure, which is measured by asecondary ion mass spectrometer (SIMS). The silicon nitride films areproduced respectively by a method of Embodiment 1 of the presentinvention and a conventional method.

FIG. 4 is a graph showing a shift in the threshold voltage (Vth) ofsemiconductor devices that are manufactured respectively by a method ofEmbodiment 1 of the present invention and a conventional method.

FIGS. 5A to 5D are cross-sectional views showing the processes of amethod for manufacturing a semiconductor device of Embodiment 2 of thepresent invention.

FIGS. 6A and 6B are graphs, each showing a hydrogen bond in siliconnitride films, which is measured by a FT-IR. The silicon nitride filmsare produced respectively by a method of Embodiment 2 of the presentinvention and a conventional method.

FIGS. 7A and 7B are graphs, each showing the hydrogen distribution ofsilicon nitride films having a polymetal gate structure, which ismeasured by a SIMS. The silicon nitride films are produced respectivelyby a method of Embodiment 2 of the present invention and a conventionalmethod.

FIG. 8 is a graph showing a shift in the threshold voltage (Vth) ofsemiconductor devices that are manufactured respectively by a method ofEmbodiment 2 of the present invention and a conventional method.

FIGS. 9A to 9D are cross-sectional views showing the processes of amethod for manufacturing a conventional semiconductor device including apolymetal gate.

FIG. 10 is a graph showing the hydrogen distribution of a conventionalsilicon nitride film having a polymetal gate structure, which ismeasured by a SIMS.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a semiconductor device of the present invention, an electricalinsulating film (also referred to as “insulating film” in the following)is formed as a layer that includes a N—H bond and substantially no Si—Hbond. The electrical insulating film is deposited on a gate electrodeformed on a gate insulating film. The layer that includes a N—H bond andsubstantially no Si—H bond is, e.g., a silicon nitride film.Specifically, when analyzed by FT-IR measurement, the layer has a peakof N—H stretching in a wave number range of 3000 to 3500 cm⁻¹ and has nopeak or a negligibly minute amount of peak of Si—H stretching in a wavenumber range of 2100 to 2500 cm⁻¹.

It is preferable that the insulating film is a deposited film obtainedby the decomposition of a mixture of a gas including substantially noSi—H bond and a gas including a N—H bond.

It is preferable that the gas including substantially no Si—H bond is atetrachlorosilane gas, and the gas including a N—H bond is at least onegas selected from the group consisting of ammonia, dimethylamine,hydrazine, and dimethylhydrazine.

The thickness of the insulating film is preferably 50 nm to 300 nm, andmore preferably 100 nm to 200 nm.

It is preferable that the gate electrode includes a polysilicon filmimplanted with boron ions, a metal film, or a laminated structure of apolysilicon film and a metal film.

The present invention can provide a semiconductor device that uses aninsulating film including substantially no Si—H bond (e.g., a siliconnitride film) as a cap film for a polymetal gate. Moreover, a gasincluding substantially no Si—H bond, e.g., tetrachlorosilane (SiCl₄,which may be abbreviated as “TCS” in the following) is used as a sourcegas for forming a silicon nitride film, thereby reducing a Si—H bond inthe silicon nitride film. Thus, less hydrogen is separated by variousheat treatments after the deposition of the silicon nitride film. Evenif hydrogen diffuses into the gate insulating film, it is possible toprevent the insulating film (e.g., a silicon nitride film) from actingas an electron trap that causes a shift in the threshold voltage (Vth)of a MOSFET and the degradation of a on-state current (Ion).

A second method for manufacturing a semiconductor device of the presentinvention includes forming a gate insulating film on a siliconsubstrate, forming a gate electrode on the gate insulating film, andforming a silicon nitride film on the gate electrode by deposition of asource gas. The source gas may be a mixture of at least one gas selectedfrom the group consisting of monosilane, dichlorosilane, andtrichlorosilane and at least one gas selected from the group consistingof ammonia, dimethylamine, hydrazine, and dimethylhydrazine. It ispreferable that the silicon nitride film is formed at temperatures of750° C. to 800° C.

In this manufacturing method, it is preferable that annealing isperformed after the formation of the silicon nitride film so that theannealing temperature is higher than the temperature at which thesilicon nitride film is formed.

A third method for manufacturing a third semiconductor device of thepresent invention includes forming a gate insulating film on a siliconsubstrate, forming a gate electrode on the gate insulating film, andforming a silicon nitride film on the gate electrode by deposition of asource gas. The source gas may be a mixture of at least one gas selectedfrom the group consisting of monosilane, dichlorosilane, andtrichlorosilane and at least one gas selected from the group consistingof ammonia, dimethylamine, hydrazine, and dimethylhydrazine. It ispreferable that annealing is performed after the formation of thesilicon nitride film so that the annealing temperature is higher thanthe temperature at which the silicon nitride film is formed.

It is preferable that the annealing temperature is 800° C. to 1200° C.,and that the annealing is performed in an atmosphere containing an inertgas, and further that the annealing is performed in an atmosphere ofreduced pressure.

In the second and the third method, it is preferable that the gateelectrode includes a polysilicon film implanted with boron ions, a metalfilm, or a laminated structure of a polysilicon film and a metal film.

The present invention allows annealing to be performed at temperatureshigher than the deposition temperature of a source gas. Therefore, evenif dichlorosilane (SiH₂Cl₂) or the like is used as the source gas forforming a silicon nitride film (a cap film for a polymetal gate), anunreacted Si—H bond in the silicon nitride film is reduced. Theannealing in an atmosphere of reduced pressure and a nitrogen gas orinert gas such as Ar particularly can reduce the unreacted Si—H bond.Thus, less hydrogen is separated by various heat treatments after thedeposition of the silicon nitride film. This makes it possible toprevent hydrogen from diffusing into the gate insulating film, acting asan electron trap, and causing a shift in the threshold voltage (Vth) ofa MOSFET and the degradation of a on-state current (Ion).

The present invention can provide a semiconductor device that isprovided with a gate cap insulating film including substantially no Si—Hbond or a semiconductor device that uses a silicon nitride filmincluding fewer Si—H and N—H bonds as a gate gap insulating film.Therefore, the diffusion of hydrogen into the polymetal gate electrodeand the gate insulating film can be suppressed to prevent a shift in thethreshold voltage of a transistor and the degradation of an on-statecurrent.

Hereinafter, specific embodiments of the present invention will bedescribed with reference to the drawings.

Embodiment 1

FIGS. 1A to 1D are cross-sectional views showing processes for forming agate cap insulating film of a semiconductor device in order, accordingto Embodiment 1 of the present invention. FIGS. 1A to 1D illustrate anexample of the fabrication of a single n-channel MOS transistor on ap-type silicon substrate using a STI process. Instead of the STIprocess, e.g., LOCOS (local oxidation of silicon) may be employed toform a region for isolating elements.

First, shallow trenches for isolation (STI) 61 are formed in a siliconsubstrate 41. The trenches 61 are produced by dry etching. Then, an nwell 51 is formed by ion implantation of phosphorus (P) and arsenic (As)into a region between the trenches (FIG. 1A).

A RTP (rapid thermal process) is performed in an atmosphere of oxygen ornitrogen to form a gate insulating film 1 having a thickness of about2.5 nm. The gate insulating film 1 is made of an oxide film oroxynitride film.

Using a LPCVD chamber, an amorphous Si film 2 is grown to have athickness of about 80 nm in a SiH₄ atmosphere, which then is doped withboron (B) by ion implantation. A titanium nitride (TiN) film 4 having athickness of about 10 nm and a tungsten (W) film 5 having a thickness ofabout 50 nm are deposited in the order mentioned. A LP-SiN film 6 (agate cap layer) having a thickness of about 150 nm is formed on thetungsten film 5 in a mixed atmosphere of tetrachlorosilane (SiCl₄) andammonia (NH₃) at 760° C.

A photoresist pattern 7 is formed to provide a gate pattern (FIG. 1B).The boron-implanted amorphous Si film 2, the titanium nitride (TiN) film4, and the tungsten (W) film 5 constitute a gate electrode 8 in thesubsequent process.

By using the photoresist pattern 7 as a mask, etching is performed toform a polymetal gate (gate electrode) 8 (FIG. 1C).

Next, a side wall 9 having a thickness of about 120 nm is formed withthe LP-SIN film. The side wall 9 is used to provide a LDD (lightly dopeddrain) structure, a source (p⁺) 71, and a drain (p⁺) 72, etc. (FIG. 1D).

The temperature at which the LP-SIN film 6 is formed ranges from 500° C.to 800° C., and preferably 700° C. to 800° C. Temperatures of not lessthan 500° C. can reduce hydrogen in the silicon nitride film, andtemperatures of not more than 800° C. can ensure the heat resistance ofthe gate electrode.

In this embodiment, a gas mixture of tetrachlorosilane and ammonia isused as a source gas for forming the film. The source gas is notparticularly limited as long as it includes substantially no Si—H bond,and can be a mixture of a tetrachlorosilane gas and a gas including aN—H bond. The deposition of this source gas results in a silicon nitridefilm that includes substantially no Si—H bond.

The gas including a N—H bond can be, e.g., ammonia, lower amine such asmonomethylamine (NH₂CH₃), hydrazine (N₂H₄), and a derivative of thesecompounds such as dimethylamine (NH(CH₃)₂) and dimethylhydrazine(CH₃NHNHCH₃).

The LP-SiN films 6 were produced respectively by a method of thisembodiment and a conventional method. Then, a hydrogen bond in each ofthe silicon nitride films was measured by a Fourier transform infraredspectrometer (FT-IR). FIG. 2 is a graph showing the results. Thehorizontal axis indicates the wave numbers, and the vertical axisindicates the absorbance. The silicon nitride film 6 of the presentinvention used a source gas of TCS (SiCl₄), while the conventional filmused a source gas of DCS (SiH₂Cl₂). As shown in FIG. 2, both the siliconnitride films 6 of the present invention and the conventional examplehad a peak of N—H stretching (ranging from 3000 to 3500 cm⁻¹). However,only the conventional film formed of DCS had a peak of Si—H stretching(ranging from 2100 to 2500 cm⁻¹). Compared with DCS (SiH₂Cl₂) and TCS(SiCl₄), this is attributed to a Si—H bond in the molecular structure ofDCS. Moreover, the bond energy of the Si—H bond is lower than that ofthe N—H bond, and thus the Si—H bond breaks easily. Consequently, thehydrogen separated from the Si—H bond may diffuse into the gateinsulating film 1, causing a shift in the threshold voltage (Vth) andthe degradation of an on-state current (Ion).

FIG. 3 is a graph showing the hydrogen distribution of the LP-SIN films6 having a polymetal gate structure, which were produced respectively bya method of this embodiment and a conventional method. The horizontalaxis indicates a depth (nm) from the surface of the LP-SiN film 6, andthe vertical axis indicates the hydrogen concentration (atoms/cm³). Thehydrogen concentration was measured by a secondary ion mass spectrometer(SIMS).

As shown in FIG. 3, the amount of hydrogen (H) in the vicinity of theinterface between the gate insulating film 1 and the polymetal gateelectrode 8 (i.e., the portion indicated by Gox in FIG. 3) is madesmaller for this embodiment (using a source gas of TCS) than for theconventional example (using a source gas of DCS). This result shows thathydrogen that has been separated from the Si—H bond diffuses into thegate insulating film 1.

FIG. 4 is a graph showing a shift in the threshold voltage (Vth) ofsemiconductor devices, which were manufactured respectively by a methodof this embodiment (a source gas: TCS, and a film forming temperature:760° C.) and a conventional method (a source gas: DCS, and a filmforming temperature: 700° C.). The horizontal axis indicates the type ofsource gas, and the vertical axis indicates the amount of shift in Vth.FIG. 4 shows that the silicon nitride film of this embodiment cansuppress a shift in the threshold voltage (Vth).

The silicon nitride film (Si₃N₄) 6 formed according to this embodimentas an insulating film on the polymetal gate 8 can suppress a shift inthe threshold voltage (Vth), which has been prominent in a conventionalsilicon nitride film. This is because the amount of hydrogen in the filmcan be reduced by using a gas that contains no hydrogen, i.e.,tetrachlorosilane (SiCl₄), thus eliminating the cause of an electrontrap. Moreover, hydrogen (H) usually is joined to a dangling bondgenerated in the manufacturing process of a semiconductor. In thisembodiment, however, the dangling bond can be terminated by halogen suchas chlorine (Cl) instead of hydrogen (H).

As described above, the silicon nitride film 6 of this embodiment isformed by using tetrachlorosilane (SiCl₄) as a source gas, therebyeffectively preventing the diffusion of hydrogen (H) into the gateinsulating film.

Embodiment 2

FIGS. 5A to 5D are cross-sectional views showing processes for forming agate cap insulating film of a semiconductor device in order, accordingto Embodiment 2 of the present invention. FIGS. 5A to 5D illustrate anexample of the fabrication of a single n-channel MOS transistor on ap-type silicon substrate using a STI process. Instead of the STIprocess, e.g., LOCOS may be employed to form a region for isolatingelements.

First, like FIG. 1A, shallow trenches for isolation (STI) 61 are formed,and then an n well 51 is formed by ion implantation of phosphorous (P)and arsenic (As) into a region between the trenches (FIG. 5A).

A RTP (rapid thermal process) is performed to form a gate insulatingfilm 1 of an oxide film or oxynitride film. Using a LPCVD chamber, anamorphous Si film 2 is grown in a SiH₄ atmosphere, which then is dopedwith boron (B) by ion implantation. A titanium nitride (TiN) film 4 anda tungsten (W) film 5 are deposited in the order mentioned. ALP-SiN film31 (a gate-cap layer) is formed on the tungsten film 5 in a mixedatmosphere of dichlorosilane (SiH₂Cl₂) and ammonia (NH₃) at 700° (in aconventional method) or 760° C. The silicon nitride film 31 is annealedfor 60 minutes under the conditions of a nitrogen atmosphere, 10² to 10⁵Pa, and 800° C. Subsequently, a photoresist pattern 7 is formed toprovide a gate pattern (FIG. 5B).

By using the photoresist pattern 7 as a mask, etching is performed toform a polymetal gate 8 (FIG. 5C).

Next, a side wall 9 is formed with the LP-SiN film 31. The side wall 9is used to provide a LDD (lightly doped drain) structure, a source (p+)71, a drain (p+) 72, etc. (FIG. 5D).

The temperature at which the LP-SIN film 31 is formed ranges from 500°C. to 800° C., preferably 700° C. to 800° C., and more preferably 750°C. to 800° C. Temperatures of not less than 700° C. can reduce theresidual hydrogen in the silicon nitride film, and temperatures of notmore than 800° C. can ensure the heat resistance of the gate electrode.

In this embodiment, a gas mixture of dichlorosilane and ammonia is usedas a source gas for forming the film. The dichlorosilane may bereplaced, e.g., by monosilane, trichlorosilane, etc. Thus, the sourcegas can be a mixture of the above silane gas and a gas including a N—Hbond.

The gas including a N—H bond can be, e.g., ammonia, lower amine such asmonomethylamine (NH₂CH₃), hydrazine (N₂H₄), and a derivative of thesecompounds such as dimethylamine (NH(CH₃)₂) and dimethylhydrazine(CH₃NHNHCH₃).

The annealing temperature is higher than the temperature at which thesilicon nitride film is formed, and desirably not less than 800° C. Theannealing temperature of not less than 800° C. can eliminate theresidual hydrogen in the silicon nitride film. It is preferable that theannealing temperature is not more than 1200° C. in view of the heatresistance of the gate electrode. The annealing time generally is 5 to120 minutes, and preferably 30 to 60 minutes. Considering the filmcharacteristics of the silicon nitride film, the annealing should beperformed in an inert gas atmosphere. Examples of the inert gas includea low reactive gas such as a nitrogen gas and a rare gas such as Ar.Although the annealing can be performed at atmospheric pressure orreduced pressure, an atmosphere of reduced pressure is preferred forreducing an unreacted Si—H bond.

The LP-SIN films 31 were produced respectively by a method of thisembodiment and a conventional method. Then, a hydrogen bond in each ofthe silicon nitride films was measured by a FT-IR. FIGS. 6A and 6B aregraphs showing the results. The horizontal axis indicates the wavenumbers, and the vertical axis indicates the absorbance. In FIG. 6A,both the silicon nitride films of this embodiment and the conventionalexample were formed by depositing DCS at 700° C. However, they differedin subsequent process, that is, the silicon nitride film of thisembodiment was annealed in a nitrogen atmosphere at 800° C. for 60minutes, while the conventional film was not annealed. In FIG. 6B, thesilicon nitride film of this embodiment was formed by depositing DCS at760° C., and the conventional film was formed by depositing DCS at 700°C. In this case, neither of the silicon nitride films was annealed.

As shown in FIG. 6A, the peak of N—H stretching (ranging from 3000 to3500 cm⁻¹) and the peak of Si—H stretching (ranging from 2100 to 2500cm⁻¹) of the silicon nitride film that has been annealed at temperatureshigher than the film forming temperature are made lower than those ofthe unannealed film.

As shown in FIG. 6B, the peak of N—H stretching (ranging from 3000 to3500 cm⁻¹) and the peak of Si—H stretching (raging from 2100 to 2500cm⁻¹) are higher than those shown in FIG. 6A. These results show thatthe N—H bond and the Si—H bond are reduced by forming the siliconnitride film at higher temperatures. The reason for this is consideredto be as follows: the film forming temperature is increased from 700° C.(the conventional example) to 760° C., and the annealing is performed attemperatures (800° C.) higher than the film forming temperature, so thatthe residual Si—H and N—H bonds in the silicon nitride film are brokento cause the diffusion of hydrogen from the silicon nitride film.

FIGS. 7A to 7B are graphs showing the hydrogen distribution of theLP-SIN films 31 having a polymetal gate structure, which were producedrespectively by a method of this embodiment and a conventional method.The horizontal axis indicates a depth (nm) from the surface of theLP-SiN film 31, and the vertical axis indicates hydrogen concentration(atoms/cm³). The hydrogen concentration was measured by a SIMS.

In FIG. 7A, both the silicon nitride films of this embodiment and theconventional example were formed by depositing DCS at 700° C. However,they differed in subsequent process, that is, the silicon nitride filmof this embodiment was annealed in a nitrogen atmosphere at 800° C.,while the conventional film was not annealed. In FIG. 7B, the siliconnitride film of this embodiment was formed by depositing DCS at 760° C.,and the conventional film was formed by depositing DCS at 700° C. Inthis case, neither of the silicon nitride films was annealed.

As shown in FIG. 7A, the amount of hydrogen (H) in the vicinity of theinterface between the gate insulating film 1 and the polymetal gateelectrode 8 is reduced by annealing the silicon nitride film attemperatures (e.g., 800° C.) higher than the film forming temperaturewhen compared to the unannealed film.

As shown in FIG. 7B, the amount of hydrogen (H) in the vicinity of theinterface between the gate insulating film 1 and the polymetal gateelectrode 8 is reduced by increasing the film forming temperature from700° C. (the conventional example) to 760° C.

FIG. 8 is a graph showing a shift in the threshold voltage (Vth) ofsemiconductor devices, which were manufactured respectively by a methodof this embodiment (a film forming temperature: 700° C., and annealingat 800° C. for 60 min.), a first comparative method (a film formingtemperature: 700° C., and without annealing), and a second comparativemethod (a film forming temperature: 700° C., and annealing at 700° C.for 60 min.). The horizontal axis indicates the conditions of annealing,and the vertical axis indicates the amount of shift in Vth. FIG. 8 showsthat the silicon nitride film that is annealed at 800° C. can suppress ashift in the threshold voltage (Vth).

The silicon nitride film (Si₃N₄) 31 formed according to this embodimentas an insulating film on the polymetal gate 8 can suppress a shift inthe threshold voltage (Vth), which has been prominent in a conventionalsilicon nitride film. This is because the amount of hydrogen in the filmcan be reduced by increasing the film forming temperature compared withthe conventional method and annealing the silicon nitride film desirablyat temperatures higher than the film forming temperature, thuseliminating the cause of an electron trap.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A semiconductor device comprising: a gate insulating film formed on asilicon substrate; and a gate electrode formed on the gate insulatingfilm; wherein the gate electrode comprises a deposited film and a gatecap insulating film formed on the deposited film, the deposited filmcomprising a polysilicon film, a metal film, or a laminated structure ofa polysilicon film and a metal film, and the gate cap insulating filmincludes a N—H bond and substantially no Si—H bond.
 2. The semiconductordevice according to claim 1, wherein the gate cap insulating film is asilicon nitride film.
 3. The semiconductor device according to claim 1,wherein the gate cap insulating film is a deposited film obtained bydecomposition of a mixture of a gas including substantially no Si—H bondand a gas including a N—H bond.
 4. The semiconductor device according toclaim 3, wherein the gas including substantially no Si—H bond is atetrachlorosilane gas, and the gas including a N—H bond is at least onegas selected from the group consisting of ammonia, dimethylamine,hydrazine, and dimethylhydrazine.
 5. The semiconductor device accordingto claim 1, wherein the polysilicon film is implanted with boron ions.6-16. (canceled)